providers/docker: don't show cmd if one is not specified
providers/docker: don't show cmd if one is not specified

Chhed13/vagrant,muhanadra/vagrant,MiLk/vagrant,darkn3rd/vagrant,ferventcoder/vagrant,wkolean/vagrant,mpoeter/vagrant,darkn3rd/vagrant,dhoer/vagrant,mkuzmin/vagrant,petems/vagrant,doy/vagrant,dhoer/vagrant,senglin/vagrant,lukebakken/vagrant,jmanero/vagrant,denisbr/vagrant,stephancom/vagrant,janek-warchol/vagrant,taliesins/vagrant,tschortsch/vagrant,BlakeMesdag/vagrant,PatOShea/vagrant,lonniev/vagrant,gbarberi/vagrant,bshurts/vagrant,taliesins/vagrant,aaam/vagrant,carlosefr/vagrant,signed8bit/vagrant,mkuzmin/vagrant,janek-warchol/vagrant,tbarrongh/vagrant,jkburges/vagrant,patrys/vagrant,jmanero/vagrant,legal90/vagrant,benh57/vagrant,mwarren/vagrant,fnewberg/vagrant,modulexcite/vagrant,petems/vagrant,PatrickLang/vagrant,kamazee/vagrant,invernizzi-at-google/vagrant,genome21/vagrant,tknerr/vagrant,loren-osborn/vagrant,aneeshusa/vagrant,tknerr/vagrant,benizi/vagrant,dustymabe/vagrant,justincampbell/vagrant,mitchellh/vagrant,muhanadra/vagrant,gajdaw/vagrant,johntron/vagrant,clinstid/vagrant,shtouff/vagrant,PatOShea/vagrant,gajdaw/vagrant,aneeshusa/vagrant,jhoblitt/vagrant,Sgoettschkes/vagrant,tschortsch/vagrant,kamigerami/vagrant,bshurts/vagrant,benizi/vagrant,shtouff/vagrant,zsjohny/vagrant,mitchellh/vagrant,Avira/vagrant,juiceinc/vagrant,wkolean/vagrant,gitebra/vagrant,Avira/vagrant,mkuzmin/vagrant,vamegh/vagrant,gajdaw/vagrant,jtopper/vagrant,stephancom/vagrant,legal90/vagrant,miguel250/vagrant,tbarrongh/vagrant,bheuvel/vagrant,obnoxxx/vagrant,ArloL/vagrant,sideci-sample/sideci-sample-vagrant,TheBigBear/vagrant,mwrock/vagrant,bryson/vagrant,teotihuacanada/vagrant,obnoxxx/vagrant,apertoso/vagrant,jfchevrette/vagrant,crashlytics/vagrant,jkburges/vagrant,tbarrongh/vagrant,carlosefr/vagrant,mwarren/vagrant,petems/vagrant,dustymabe/vagrant,krig/vagrant,petems/vagrant,signed8bit/vagrant,jkburges/vagrant,Avira/vagrant,kamazee/vagrant,gpkfr/vagrant,BlakeMesdag/vagrant,tschortsch/vagrant,tbriggs-curse/vagrant,janek-warchol/vagrant,bheuvel/vagrant,gbarberi/vagrant,blueyed/vagrant,tknerr/vagrant,evverx/vagrant,cgvarela/vagrant,jhoblitt/vagrant,h4ck3rm1k3/vagrant,tjanez/vagrant,bshurts/vagrant,iNecas/vagrant,jean/vagrant,modulexcite/vagrant,Avira/vagrant,tomfanning/vagrant,PatrickLang/vagrant,ArloL/vagrant,lukebakken/vagrant,otagi/vagrant,jmanero/vagrant,mwarren/vagrant,mwrock/vagrant,otagi/vagrant,TheBigBear/vagrant,dhoer/vagrant,chrisroberts/vagrant,rivy/vagrant,mkuzmin/vagrant,blueyed/vagrant,TheBigBear/vagrant,kamigerami/vagrant,ianmiell/vagrant,teotihuacanada/vagrant,dharmab/vagrant,mwrock/vagrant,juiceinc/vagrant,dharmab/vagrant,signed8bit/vagrant,bryson/vagrant,genome21/vagrant,h4ck3rm1k3/vagrant,zsjohny/vagrant,jtopper/vagrant,doy/vagrant,sni/vagrant,wangfakang/vagrant,MiLk/vagrant,sax/vagrant,nickryand/vagrant,kalabiyau/vagrant,muhanadra/vagrant,jberends/vagrant,kamazee/vagrant,clinstid/vagrant,marxarelli/vagrant,denisbr/vagrant,Chhunlong/vagrant,zsjohny/vagrant,sax/vagrant,sax/vagrant,h4ck3rm1k3/vagrant,kamigerami/vagrant,tbarrongh/vagrant,stephancom/vagrant,evverx/vagrant,philwrenn/vagrant,lonniev/vagrant,marxarelli/vagrant,tjanez/vagrant,Endika/vagrant,philoserf/vagrant,dhoer/vagrant,myrjola/vagrant,stephancom/vagrant,TheBigBear/vagrant,bdwyertech/vagrant,pwnall/vagrant,tbriggs-curse/vagrant,bdwyertech/vagrant,patrys/vagrant,justincampbell/vagrant,jean/vagrant,krig/vagrant,marxarelli/vagrant,modulexcite/vagrant,philoserf/vagrant,tbriggs-curse/vagrant,bshurts/vagrant,miguel250/vagrant,krig/vagrant,tomfanning/vagrant,pwnall/vagrant,apertoso/vagrant,gpkfr/vagrant,sax/vagrant,jberends/vagrant,gpkfr/vagrant,vamegh/vagrant,taliesins/vagrant,invernizzi-at-google/vagrant,jtopper/vagrant,mpoeter/vagrant,justincampbell/vagrant,fnewberg/vagrant,dharmab/vagrant,kalabiyau/vagrant,johntron/vagrant,crashlytics/vagrant,signed8bit/vagrant,Chhed13/vagrant,jhoblitt/vagrant,miguel250/vagrant,wangfakang/vagrant,BlakeMesdag/vagrant,ArloL/vagrant,aaam/vagrant,wkolean/vagrant,philwrenn/vagrant,benh57/vagrant,tjanez/vagrant,crashlytics/vagrant,tomfanning/vagrant,jfchevrette/vagrant,lonniev/vagrant,tjanez/vagrant,darkn3rd/vagrant,dharmab/vagrant,tknerr/vagrant,teotihuacanada/vagrant,invernizzi-at-google/vagrant,shtouff/vagrant,genome21/vagrant,legal90/vagrant,iNecas/vagrant,jean/vagrant,chrisvire/vagrant,vamegh/vagrant,iNecas/vagrant,ianmiell/vagrant,benizi/vagrant,jmanero/vagrant,jtopper/vagrant,benh57/vagrant,bheuvel/vagrant,jfchevrette/vagrant,shtouff/vagrant,bdwyertech/vagrant,aneeshusa/vagrant,kalabiyau/vagrant,vamegh/vagrant,dustymabe/vagrant,ferventcoder/vagrant,nickryand/vagrant,kamigerami/vagrant,zsjohny/vagrant,teotihuacanada/vagrant,juiceinc/vagrant,jhoblitt/vagrant,bryson/vagrant,jkburges/vagrant,bdwyertech/vagrant,gbarberi/vagrant,senglin/vagrant,pwnall/vagrant,aneeshusa/vagrant,cgvarela/vagrant,tbriggs-curse/vagrant,Endika/vagrant,tschortsch/vagrant,h4ck3rm1k3/vagrant,cgvarela/vagrant,ferventcoder/vagrant,loren-osborn/vagrant,Endika/vagrant,blueyed/vagrant,doy/vagrant,lukebakken/vagrant,genome21/vagrant,channui/vagrant,Chhunlong/vagrant,benh57/vagrant,jfchevrette/vagrant,Sgoettschkes/vagrant,justincampbell/vagrant,aaam/vagrant,theist/vagrant,janek-warchol/vagrant,sideci-sample/sideci-sample-vagrant,sideci-sample/sideci-sample-vagrant,senglin/vagrant,cgvarela/vagrant,senglin/vagrant,ArloL/vagrant,muhanadra/vagrant,loren-osborn/vagrant,otagi/vagrant,PatrickLang/vagrant,tomfanning/vagrant,gitebra/vagrant,philoserf/vagrant,legal90/vagrant,Endika/vagrant,ianmiell/vagrant,Chhunlong/vagrant,modulexcite/vagrant,taliesins/vagrant,loren-osborn/vagrant,otagi/vagrant,Chhed13/vagrant,philwrenn/vagrant,chrisroberts/vagrant,miguel250/vagrant,chrisroberts/vagrant,gitebra/vagrant,myrjola/vagrant,johntron/vagrant,sni/vagrant,sni/vagrant,lukebakken/vagrant,theist/vagrant,aaam/vagrant,chrisvire/vagrant,carlosefr/vagrant,carlosefr/vagrant,philoserf/vagrant,Chhunlong/vagrant,denisbr/vagrant,rivy/vagrant,invernizzi-at-google/vagrant,theist/vagrant,patrys/vagrant,krig/vagrant,theist/vagrant,chrisroberts/vagrant,gitebra/vagrant,apertoso/vagrant,mitchellh/vagrant,johntron/vagrant,channui/vagrant,evverx/vagrant,obnoxxx/vagrant,kalabiyau/vagrant,channui/vagrant,fnewberg/vagrant,wangfakang/vagrant,crashlytics/vagrant,darkn3rd/vagrant,myrjola/vagrant,fnewberg/vagrant,Chhed13/vagrant,benizi/vagrant,PatrickLang/vagrant,gpkfr/vagrant,wkolean/vagrant,jberends/vagrant,ferventcoder/vagrant,philwrenn/vagrant,PatOShea/vagrant,mpoeter/vagrant,rivy/vagrant,myrjola/vagrant,clinstid/vagrant,chrisvire/vagrant,sni/vagrant,nickryand/vagrant,PatOShea/vagrant,doy/vagrant,kamazee/vagrant,mitchellh/vagrant,pwnall/vagrant,denisbr/vagrant,ianmiell/vagrant,MiLk/vagrant,dustymabe/vagrant,jberends/vagrant,bheuvel/vagrant,bryson/vagrant,blueyed/vagrant,gbarberi/vagrant,mpoeter/vagrant,jean/vagrant,nickryand/vagrant,wangfakang/vagrant,patrys/vagrant,marxarelli/vagrant,Sgoettschkes/vagrant,mwarren/vagrant,Sgoettschkes/vagrant,mwrock/vagrant,juiceinc/vagrant,rivy/vagrant,lonniev/vagrant,apertoso/vagrant,chrisvire/vagrant